Elements of the tobacco plant are known to comprise a proportion of lipids, a component of varying composition, variously defined but most commonly referenced for convenience as included within the hydrocarbon solvent extractables, e.g. from petroleum ether or hexane.
Recently lipids have occasioned interest in the continuing analysis of health related aspects of the use of tobacco. Specifically, it has been suggested that the hydrocarbon solvent solubles contribute to the generation of polynuclear aromatic hydrocarbons during leaf pyrolysis. Experimental results demonstrate that about 70% of the aromatic hydrocarbons, ranging from benzene to benz(.alpha.)pyrene in the pyrolysates, are due to leaf components extractable with hexane and acetone, although these extracts amount to less than 25% of dry leaf weight. See "Studies on the Pyrogenesis of Tobacco Smoke Constituents: A Review" Chortyk, O. T. and Schlotzhauer, W. S. Beitrage zur Tabakforschung (Vol. 7, No. 3, Nov. 1973, pp. 165-177).
There are numbers of lipid fractions characterized by the extraction technique characterized by the extraction technique employed. The neutral lipids (commonly defined by high solubility in chloroform) form the major portion of tobacco leaf lipid material, comprising about 60-75% of the total. (Further, leaf comprises the highest proportion of lipids, at 6-8% absolute in lamina, compared to about 1% absolute in stalk and midribs, respectively). Unfortunately, any solvent extraction inevitably removes additional chemical substituents, often those which contribute favorably to taste and aroma. Accordingly, other methods for lipid removal are of interest.
A proportion of lipids may be observed on tobacco leaf surfaces and, in general, their composition is somewhat different than the so-called internal lipids. It is these surface lipids which are commonly referred to as neutral lipids, resins or waxes, and are generally associated with the glandular trichomes (hairs) which cover the leaf surface and the cuticle layer just beneath these hairs.